1. Field of the Invention
The present invention relates to a method of producing a hollow or solid carbon fiber with an active surface in a solution or in an atmosphere of a saturated vapor of a solution.
2. Related Background Art
A number of hollow or solid fibers, such as a carbon nanotube (CNT), a carbon nanofiber (CNF) or a carbon fiber (CF), are known. In order to produce these fibers, it is necessary to expose a depressurized gas to a high temperature of 500° C. or more (for instance, see Japanese Patent Application Laid-Open Nos. H5-125619; H5-229809; H6-157016; H8-13254; H8-134724; H9-241929; 2000-95509; 2001-19413; and 2001-80913). Further, a high temperature of 900° C. or more may be necessary for producing the fibers (for instance, see Japanese Patent Application Laid-Open No. 2003-12312). Such materials have been considered to be capable of greatly improving their mechanical characteristics, electrical characteristics and the like by being combined with plastic, ceramic, rubber, metal material, or the like. Various researches have been conducted to explore this issue.
Carbon nanotubes, carbon nanofibers, carbon fibers or the like, which can be produced by these methods, have very few active sites on the fiber surfaces, resulting in gaps between the fibers and plastic, ceramic, rubber, metal, or the like. Thus, the combinations have not been able to fully achieve the original purpose. In order to overcome these deficiencies, several methods, such as an oxidization treatment and a mechanical treatment, have been proposed as surface-activating methods (for instance, see Japanese Patent Application Laid-Open Nos. H5-9812; H5-179514; and H6-212517).
However, because these methods involve a heat treatment at a high temperature of 500° C. or more, they have difficulties in stably producing surface-activated carbon nanotubes, carbon nanofibers or carbon fibers.